Phytotaxa 188 (4): 181–197 ISSN 1179-3155 (print edition) www.mapress.com/phytotaxa/ PHYTOTAXA Copyright © 2014 Magnolia Press Article ISSN 1179-3163 (online edition) http://dx.doi.org/10.11646/phytotaxa.188.4.1 Lactarius subgenus Russularia (Russulaceae) in South-East Asia: 2. Species with remarkably small basidiocarps KOMSIT WISITRASSAMEEWONG1,2,3, JORINDE NUYTINCK4, FELIX HAMPE3, KEVIN D. HYDE1,2 & ANNEMIEKE VERBEKEN3 1Institute of Excellence in Fungal Research, Mae Fah Luang University, 333 Moo 1, Thasud sub-district, Muang district, Chiang Rai 57100, Thailand, E-mail: [email protected] (corresponding author) 2School of Science, Mae Fah Luang University, 333 Moo 1, Thasud sub-district, Muang district, Chiang Rai 57100, Thailand 3Research Group Mycology, Department of Biology, Gent University, K.L. Ledeganckstraat 35, 9000 Gent, Belgium 4Naturalis Biodiversity Center, Section National Herbarium of the Netherlands, P.O. Box 9517, 2300RA Leiden, The Netherlands Abstract This paper is the second in a series of biodiversity papers on Lactarius subgenus Russularia in tropical forests of Southeast Asia. This study is based on extensive mycological exploration, especially in Northern Thailand, during the past ten years. In this paper we consider some species that are characterized by remarkably small basidiocarps i.e. with an average pileus diameter that is smaller than 20 mm. One of the most common species in Northern Thailand with dwarf basidiocarps is L. gracilis, originally described from Japan. We introduce the new species L. crenulatulus, L. perparvus and L. glabrigracilis with morphological descriptions and illustrations. Molecular evidence based on the ITS sequence analysis supports the clas- sification and novel status of the taxa. All species are associated with trees belonging to the Fagaceae. These are the first reported collections of small basidiocarps of L. subg. Russularia in Southeast Asia. In our paper we compare these new spe- cies with small basidiocarp with similar representatives from Europe and other Asian regions. Keywords: milkcaps, taxonomy, molecular phylogeny Introduction In the recent classification of Lactarius Pers. (Buyck et al. 2010), three subgenera, L. subg. Lactarius (Fr. ex J. Kickx f.) Kauffman, L. subg. Russularia (Fr.) Kauffman and L. subg. Plinthogalus (Berk.) Hesler & A.H. Sm. were recognized. Among these three subgenera, L. subg. Russularia is assumed to be a taxonomically complex group which is widely distributed in temperate and tropical regions, but poorly represented in tropical Africa and South America (Verbeken 1996, Verbeken & Walleyn 2010; Wisitrassameewong et al. 2014). In Southeast Asia, 13 species have been reported in L. subg. Russularia, mainly from Indonesia (Verbeken et al. 2001), Southern China (Wang 2000, Wang & Liu 2002) and Malaysia and Thailand (Wisitrassameewong et al. 2014). Studies have also reported and described taxa from subg. Russularia in other regions of Asia, e.g. in Japan by Hongo (1957a, 1957b, 1971), in Papua New Guinea (Verbeken & Horak 2000), in the Himalaya region, India by Das et al. (2004) and Joshi et al. (2012). Chinese type specimens, including representatives of this subgenus, have been re-evaluated because European and American names were misapplied (Wang 2007). L. squamulosus Z.S. Bi & T.H. Li was considered a synonym of L. gracilis Hongo. Up to now all species known in Asia are endemic for the continent and the use of American and European names could not be justified. Macromorphologically, most members of leave out subg. Russularia can be recognized by their dry pileus surface and colours that are typically dominated by shades of orange and reddish brown to brown. The latex color and color changes are not as variable as in the other subgenera of Lactarius, with most species having white or whitish and unchanging latex. In a few species however, the latex is yellow (Verbeken et al. 2001, Das et al. 2004) and in some the latex changes from white to cream or yellow. An exceptional species is L. sulphurescens Verbeken & E. Horak from Java, Indonesia (but also occurring in Malaysia), that has abundant, spectacular, golden yellow latex (Verbeken et al. 2001). In some species, such as L. stubbei Wisitrassameewong & Verbeken, the color change only becomes visible when the latex is drying, then showing a clear pale yellow tinge (Wisitrassameewong et al. 2014). Spore ornamentation and pileipellis structure are microscopic characters that discriminate between species. The spore ornamentation is typically an incomplete to complete reticulum while spiny or obtuse isolated warts occur in some species. The pileipellis structure shows a wide variety, Accepted by Gareth Jone: 11 Sept. 2014; published: 15 Dec. 2014 181 References Buyck, B., Hofsetter, V., Verbeken, A. & Walleyn, R. 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